The present invention relates to a driver for a switching device.
A driver for driving a switching device, such as a metal-oxide-semiconductor field-effect-transistor (a “MOSFET”), a bipolar transistor and an insulated gate bipolar transistor (an “IGBT”), is widely used for an inverter and a switching source. Referring to FIGS. 4 and 10, for example, in a switching circuit, as a driver 10 supplies an electric charge to a control terminal or a gate 11g of a switching device 11 so as to increase a control voltage Vgs above a predetermined value, electric current Id passes between a drain 11d and a source 11s. On the other hand, as the driver 10 draws an electric charge from the control terminal 11g so as to decrease the control voltage Vgs below another predetermined value, the switching device 11 turns off. Thus, the electric current Id is controlled by regulating the control voltage Vgs.
When the control voltage Vgs varies rapidly, a voltage surge is occurred between the drain 11d and the source 11s mainly due to an inductance component L of a load circuit. As a result, the switching device itself collapses or electromagnetic noise is generated to affect external electronic instruments.
In the prior art, to regulate a voltage surge, an electrical resistance R having an appropriate value of resistance is connected to the control terminal 11g so that the control voltage Vgs slowly varies when switching is performed. Incidentally, as the value of the electrical resistance R is greater, the control voltage Vgs varies more slowly.
When the greater value of the electrical resistance R which is connected to the control terminal 11g is applied, the voltage surge is more effectively regulated. However, a switching loss on the switching device 11 which turns into heat also increases so as to cause troublesome. That is, the voltage surge regulation and the heat generation have a trade-off relation with each other.
Meanwhile, depending on a usage of the switching device, there may be various operation status. Some mainly regulate electromagnetic noise while permitting the heat generation to a certain extent, or the others mainly regulate the heat generation while permitting the electromagnetic noise to a certain extent. In this state, the value of the electrical resistance R is previously configured in such a manner that both the electromagnetic noise and the heat generation are in a permissible range in all operation conditions. Therefore, the degree of freedom on design is limited, and the resistance value is difficult to select so as to perform inherent function of the switching device. Accordingly, there is a need for a driver for a switching device to widen the degree of freedom on design.